1. Field of the Invention
The present invention relates to an apparatus for reducing impulse noise, and more particularly, to an apparatus for reducing impulse noise using a median filter, and a method thereof.
2. Description of the Related Art
In general, an image signal includes impulse noise, the amplitude of which changes irregularly according to external or internal conditions. Thus, an image reproducing apparatus must remove the impulse noise to obtain an image of high quality.
FIG. 1 is a block diagram showing a typical impulse noise reduction apparatus.
An image signal consists of pixels. The mean of the image signal is obtained by determining a window of n pixels, e.g., five pixels a1, a2, a3, a4 and a5 in FIG. 1. Here, a5 is a mid.sub.-- value. A subtractor 120 subtracts the mid.sub.-- value 114 from the mean 112 and transmits the value to a comparator 130. The comparator 130 compares the value obtained from the subtractor 120 with a reference value. If the value is higher than the reference value, a first level, e.g., logic high, which indicates noise, is output, and if not, a second level, e.g., logic low, which indicates normal pixel data, is output. A multiplexer 140 selects either the mid.sub.-- pixel 114 or the mean 112 according to the level applied by the comparator 130, and outputs the selected value. When the first level is applied, the mean 112 is selected and output.
However, the apparatus of FIG. 1 interprets high-frequency components 210 of the image signal as impulse noise, and thus selects the mean of the pixels corresponding thereto as shown in FIG. 2A, outputting an image signal having a deteriorated high-frequency component 220 as shown in FIG. 2B. Accordingly, the image signal obtained by the apparatus of FIG. 1 has deteriorated frequency characteristics, and therefore lower resolution.